What
Is a Urine Concentration Test?

A urine concentration test determines how well your kidneys are
functioning. The test may be used to test your kidneys’ response to:

too much fluid intake (water loading)

too little fluid intake (dehydration)

a hormone that should concentrate your urine,
antidiuretic hormone (ADH)

You may take the test several times under different
circumstances.

The test itself is painless and all you have to do is provide a
clean-catch urine sample. However, the preparation phase may be uncomfortable.

What
is the Purpose of a Urine Concentration Test?

Your doctor may recommend urine concentration testing if you are
urinating too much or too little. The test can help identify specific types of
problems with your kidneys.

The main reason this test is ordered is to see if you are
suffering from central diabetes insipidus — a disease that causes excessive
urination. This form of diabetes can occur when a head injury affects how your
brain releases antidiuretic
hormone (ADH). ADH normally increases the amount of water the kidneys
retain. In central diabetes insipidus, your brain does not release enough ADH.

A urine concentration test can also be used to evaluate:

dehydration

kidney failure

heart failure

other hormone problems

complications of a urinary tract infection

How
Is the Test Performed?

The test is based on a lab analysis of your urine.

Preparing for the Test

Depending on how the lab plans to analyze your urine, before the
test you may be asked to:

drink excess fluids

avoid fluids for a period of time

take ADH (which can be taken in either pill form
or a nasal spray).

Taking a Clean-Catch Urine Sample

The urine concentration test requires a clean-catch urine sample.
The goal of a clean catch is to avoid contaminating the urine sample with
bacteria from your skin. You will be given a moist towelette and a specimen cup
for the collection.

Wash your hands thoroughly with soap and warm water. Open the
collection cup. Place the lid on a clean surface. Be careful not to touch the
inside of the cup or the inside of the lid.

Use the moist towelette to clean the area around your urethra.
Then begin to urinate into the toilet. After a few seconds, put the cup in your
urine stream. Once you have collected enough urine, remove the cup. Finish
urinating into the toilet. Then carefully recap the cup, being careful not to
touch the inside of the container or lid.

Return the cup as instructed by your doctor. Your urine will be
sent to a lab for testing.

Interpreting
the Results of Your Urine Concentration Test

The laboratory will test how concentrated your urine is. More
concentrated urine means that there are more solutes and less water in the
sample. Solutes are dissolved particles, such as sugars, salts, and proteins.

Normal values may vary based on the laboratory used. However,
typically, your urine is measured in specific gravity — the ratio of the
density of your urine to the density of water (1.000). Normal values tend to be
in the range of at and slightly above the density of water (1.000 to 1.030).
Your urine should be more concentrated after being given ADH.

If your urine is very concentrated, your doctor may suspect one
or more of the following conditions:

dehydration

diarrhea

excess sweating

glycosuria (too much sugar in your urine)

heart failure

narrowing of the renal arteries

inappropriate ADH secretion

excess vomiting

fluid restriction

Low urine concentration suggests:

too much fluid intake

diabetes insipidus

kidney failure

pyelonephritis

Combining multiple test preparations can help your doctor
determine if your diabetes insipidus is due to a head injury and a resulting
lack of ADH production, or because your kidneys can’t properly respond to ADH (this
condition is called nephrogenic diabetes insipidus).

Potential
Side Effects of Taking the Test

This test is not associated with any adverse side effects.
However, refraining from drinking fluids for the test may make you feel
dehydrated. Once the test is completed, ask your doctor if you can resume
drinking fluids. This will rehydrate your body.